Medical lasers should be designed to meet safety standards to mitigate primarily against, for example, inadvertent laser exposure to body parts, over exposure with the laser treatment and single component failure. To achieve these safety standards the currently accepted standard is to utilize an electronically controlled mechanical shutter and photodetectors to deliver the laser output as shown in FIG. 1.
Mechanical shutters have proven to be slow and potentially unreliable. The mechanism of action for a mechanical shutter it to control movement and maintain a mechanical obstacle in and out of the laser beam path to prevent treatment laser light being delivered to the treatment region or even existing the laser enclosure within the device, until appropriate conditions are achieved for laser delivery. At turn-on of the device the mechanical shutter is initially “closed” (or moved into the closed position), blocking the laser output beam. Upon appropriate conditions the shutter is moved from the “closed-to-open” position, and maintained in the “open” position to allow laser delivery and treatment. Upon a second set of conditions the shutter is moved from the “open-to-closed” position, and maintained in the closed position to prevent laser delivery and treatment. Some mechanical shutters include a laser absorber to absorb the laser energy and/or a reflector to redirect the laser energy from the laser beam path to a beam dump.
The movement from “open-to-closed” (or visa versa) is usually on the order of at least tens of milliseconds as a result of the movement of mass from a stationary position to a different stationary position and accounting for acceleration, deceleration and “de-bouncing”, coming to rest in the secondary stationary position. Position sensors are typically required to confirm the shutter is in an “open”, “closed” or “transition” state, and often redundancy is built around the sensor and/or the shutter itself. Mechanical shutters are based on moving parts and as such subject to wear and tear and potentially sticking in either the “closed” and even more dangerous the “open” positions, resulting in an error conditions and device failures.
A typical traditional system performs a test of safety mitigations at start-up of the device with the mechanical shutter in a “closed” position, blocking external laser exposure. Such a test involves the operation of laser emission, the operation of photodetectors and test of the calibration data. In normal operation, when the user does not intend to use the laser device, the system is in Standby Mode and the mechanical shutter is closed preventing inadvertent exposure. When the user desires that the laser may be used, the user selects the Ready Mode and the mechanical shutter is opened. The user can then activate the laser emission by depressing the Laser Activation Switch.
Photodetector signals are monitored by a Safety Monitor Circuit to manage over power traditional medical laser systems. If over power is detected by the Safety Monitor Circuit, the mechanical shutter will be closed. Again, the time scale to stop this over power situation is at least tens of milliseconds, and hence is one of the weaknesses of using mechanical shutters.
To mitigate single component failure in traditional medical laser a duplication of power monitoring and safety circuits is used. Accordingly, traditional medical lasers have redundant photodetectors, internal switches in the Laser Activation Switch and redundancy on the mechanical shutter and/or sensors within.
The design of medical lasers has evolved from high voltage systems to drive gas lasers and arc lamps to pump the laser material, to high current diodes for direct laser emission and/or to pump laser material. Coming from a high voltage origin, where current sensors are not used and switching in the main electrical path are not encouraged, safety mitigations were put in place such as the mechanical shutter to block the laser light, and primary safety monitoring was done with photodetectors to monitoring the laser light directly. In particular, the mechanical shutter and photodetectors have persisted with time and through the evolution of medical laser designs, further the additional cost, design complexity and safety monitoring have previously precluded the need to build further redundancy and the concept of removing the mechanical shutter has not been implemented to date.
An alternative to a mechanical shutter is an optical shutter (for example a Pockels Cells). Rather than moving a mechanical object into the beam path to control the transmission of laser energy, an optical component is placed in the beam path which have the ability to switch from optically opaque to optically transparent. Optically opaque is analogous to a “closed” shutter position in case of a mechanical shutter blocking the laser treatment beam and optically transparent, is analogous to an “open” shutter position in case of a mechanical shutter, allowing the laser energy to be delivery to the treatment region. Optical shutters are typically expensive and have the potential of being damaged at the laser power levels utilized for medical treatments and as such are not utilized in medical laser devices.
Accordingly, there is a need in the art to develop new techniques other than mechanical or optical shutters for monitoring and safely controlling the laser output during medical laser treatments. The focus of the present invention is a medical laser device that utilizes an electronic shutter and does not include a mechanical or an optical shutter.